Motor deficits are common after stroke and are a major contributor to stroke-related disability. Recent studies suggest the potential to improve motor status weeks-years after stroke. The proposed study aims to use repetitive transcranial magnetic stimulation (rTMS) to modify cortical activity in patients with a history of weakness-inducing subcortical stroke. An advantage of this approach is that it is local rather than systemic. Also, if found safe and useful, rtMS might be combined with pharmacological approaches in future studies. The intervention in the current study is rTMS at a frequency (20 Hz) known to facilitate motor cortex activity. The rTMS target is the hand motor area on stroke-side motor cortex. Several studies suggest that the amount of stroke-hemisphere motor cortex active during attempted movement is of paramount importance to motor outcome. In particular, facilitating motor cortex ventral or anterior to the hand motor area is hypothesized to best facilitate motor cortex via rTMS and thereby improve arm motor status. Image-guided methods are a central feature of the proposal, and will improve the precision and reliability of rTMS application: frameless stereotactic methods will be used to target cortical stimulation. The proposed study is a phase I, 2 site, 2 dose-tier, double-blinded study with concurrent controls that will evaluate the safety of 20 Hz rTMS in the treatment of patients with hemiparesis chronically after subcortical stroke. Study entry critiera are geared towards maximum safety, for example, enrolling only those with subcortical stroke, the patient subgroup in whom this intervention is most likely to be safe. Though the primary focus of this study is safety, pilot data will be collected regarding potential clinical efficacy. As such, occupational therapy will accompany rTMS, as numerous studies have established that a plasticitypromoting intervention best improves motor outcome when accompanied by relevant motor experience. The primary goal of the proposed study is to establish the safety of this image-guided method in this population-an appropriate first step for any new therapeutic intervention. Secondarily, the study is designed to detect any possible trends towards clinical efficacy. The long-term goal of these studies is to develop a safe and efficacious method for facilitating motor cortex function in order to improve motor status of patients with stroke-related weakness.